Safety evaluation of defective polyethylene pipe under point load: Load ratio calculation method based on J-integral criterion

Abstract

Natural settlement of the ground can cause hard objects (such as stones or tree roots) in the soil to press against the surface of buried polyethylene (PE) pipelines, resulting in point load that lead to stress concentration, indentation deformation, and in severe cases, rupture and fracture failure of the pipelines. In this study, the constitutive parameters and fracture toughness J_IC of PE materials were measured and verified. To investigate the safety impact of point loads on PE gas pipelines with defects, the failure behavior and fracture morphology of PE pipes under point load conditions were analyzed through laboratory experiments. Additionally, the failure assessment diagram (FAD) method was employed to assess the safety of defective PE pipes. The FAD comprises failure assessment curves (FAC) and failure assessment parameters (including the fracture ratio K_r and load ratio L_r), and the selection of FAC and the calculation method for K_r were determined. Given the limitations of existing L_r calculation methods, a novel approach based on the elastic–plastic J-integral was proposed to calculate L_r. This method was refined and validated through finite element analysis results and experiments. Furthermore, a finite element model of a buried PE pipeline with a semi-elliptical crack under point load was established to analyze the influence of factors such as the size of hard objects, internal pipeline pressure, pipeline diameter, and defect size on the mechanical behavior of PE pipes. Safety assessments of the pipeline were then conducted using the FAD method. This research provides valuable insights and a reference for the safety assessment of buried PE pipelines with defects.